1. Field of the Invention
The present invention relates to a carbon anode for a secondary battery employing a carbon as an active material.
2. Description of the Related Art
Graphite forms an intercalation compound which has regularly stacking layer. By using this structure, graphite has been studied as an anode for a secondary battery. Then, it is found that in a case where it is used in an electrolyte, for example, a carbon material of low crystallinity such as a carbon material (disclosed in Japanese Opened Patent No. 24555/1988) which is obtained by pyrolytically decomposing a hydrocarbon in a vapor phase and has a turbostratic structure and peculiar orientation is preferably used.
However, in a case of the carbon material of low crystallinity, a potential of battery is largely varied as dopant is undoped. It is because capacity which can be used as a battery anode is reduced, and then it is difficult to produce a battery of high capacity.
In fact, it is found that the variation in the potential is smaller and capacity which can be used as the battery anode is increased in a carbon material of higher crystallinity among carbon materials.
However, as the crystallinity increases, it is supposed that charging efficiency is reduced because of decomposition of the electrolyte, and then the carbon structure (referring to J. Electrochem. Soc., 117, 222, (1970)). Such reduction of the charging efficiency is observed, for example, at a shoulder of potential curve in a case where the variation in potential vs. a charge amount divided by initial charging is plotted. The decomposition of the carbon structure is indicated by reduction of cyclic characteristics.